Rice Pi5-Mediated Resistance to Magnaporthe oryzae Requires the Presence of Two Coiled-Coil-Nucleotide-Binding-Leucine-Rich Repeat Genes

Abstract

Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most devastating diseases of rice. To Understand the molecular basis of PO mediated resistance to M. oryzae, we cloned the resistance (R) gene at: this locus using a map-based cloning strategy. Genetic and phenotypic analyses of 2014 F-2 progeny from a mapping population derived from a cross between IR50, a susceptible rice cultivar, and the RIL260 line carrying Pi5 enabled its to narrow down the Pi5 locus to a 130-kb interval. Sequence analysis of this genomic region identified two candidate genes, Pi5-1 and Pi5-2, which encode proteins carrying three motifis characteristic of R genes: an N-terminal coiled-coil (CC) motif, a nucleotide-binding (NB) domain, and a leucine-rich repeat (LRR) motif. In genetic transformation experiments of a susceptible rice cultivar, neither the Pi5-1 nor the Pi5-2 gene was found to confer resistance to M. oryzae. In contrast, transgenic rice plants expressing both of these genes, generated by crossing transgenic lines carrying each gene individually, conferred Pi5-mediated resistance to M. oryzae. Gene expression analysis revealed that Pi5-1 transcripts accumulate after pathogen challenge, whereas the Pi5-2 gene is constitutively expressed. These results indicate that the presence of these two genes is required for rice Pi5-mediated resistance to M. oryzae.